‘Most parents think all germs are bad, that is not true. Most will just stimulate your immune system and make you stronger,’ Prof Gilbert told The Independent.

‘Sterilising your home like a hospital could lead your child to have a severely hyper sensitized immune system leaving them open to allergies and asthma, even neurodevelopmental problems.

‘Rescue a dog, let them eat food off the floor, play in the soil, dirt is Good!’

Scientists believe that without exposure to dirt and germs early in life, the immune system doesn’t learn how to control its reaction to everyday invaders such as dust and pollen.

This can result in it ‘mis-firing’ later in life, leading to allergies and other illnesses.

When children play in the garden in mud, it’s not necessary to immediately sterilise their hands or faces, according to Prof Gilbert, who is director of the Microbiome Centre at the University of Chicago.

Worries that pets will pass on germs to youngsters are also unfounded, he said.

In fact, when a dog licks a child’s face it is beneficial for their immune system rather than harmful, he explained. Even faeces, as unpalatable as it is, is ‘generally harmless’ thanks to vaccination and general sanitation our homes.

However he does warn to be careful cooking and handling meat, as raw it contains many disease-carrying pathogens.According to Prof Gilbert, the immune systems of our ancestors’ children were more robust compared to today.

This is because they had a more relaxed attitudes to germs and their bodies were strengthened by a multitude of microbial interactions, he said.

To support his theory, Prof Gilbert studied the immune profiles of Amish children – who lead a very simplistic lifestyle free of the modern conveniences in which farming plays a big role.

His 2016 research found significantly lower rates of asthma among youngsters who lived on small farms that were ‘rich in microbes.’

Now, when there aren’t enough, the immune system starts to age, Prof Gilbert said, which can increase the chances of allergic responses.

Avoid hand sanitizers and opt for fermented foods. Hand sanitizer are more damaging to a child’s health than soapy water, Prof Gilbert also claims. Parents should also give their children more fermented foods which contain bacteria.

The microflora that lives in fermented foods, creates a protective lining in the intestines and shields it against pathogenic factors, such as salmonella and E.coli.